11 It is remarkable that Methodius' vigilant love had crossed the borders of Moravia and reached the Liburnians and Serbs, since he was Cyril's successor. Now it reached the Pannonians, whose prince, Kocel, he disposed to the Catholic religion and retained in his duties. It also reached the Bulgarians, whom he confirmed in the faith along with their leader Boris. Then he dispensed the gifts of heaven to the Dalmatians. Finally, he worked strenuously that the Carinthians might be brought to the knowledge and the worship of the one true God.
Source: Grande Munus (Vatican.va)